I’m not sure that this is supported feature with TightVNC. Step 5 is about creating systemd service and nothing about transferring files. This step will ensure that you can manage VNC server (start and stop it mostly) via systemd commands:

sudo systemctl start myvncserver.service

sudo systemctl stop myvncserver.service

sudo systemctl restart myvncserver.service

Also this will let you startup VNC server automatically when you reboot Droplet.
As you see, nothing to do with file transfers.

However, you can use some other utilities for transferring files, like WinSCP, which is great tool. You can also set up sFTP or something similar. Maybe if someone got it working can share his experience, but I don’t thing it’s supported.